Radio frequency communication systems are typically allocated a radio frequency spectra over which system users transmit and receive information. As the number of users of radio frequency communication systems increase, the usable radio frequency spectra is becoming increasingly scarce. In many regions of the United States, for example, the radio frequency spectrum set aside for cellular telephone users has already become saturated to such an extent that cellular subscribers must often wait for an available radio frequency channel. As the number of cellular subscribers increases, users will experience increasingly longer delays in obtaining an available channel.
In addition to existing systems, such as cellular systems, new two-way communication systems are planned which will require additional radio frequency spectrum. As these new systems are implemented, subscribers to the new systems will further crowd the usable radio frequency spectra.
One method for more efficiently utilizing the currently available radio frequency spectra is to share allocated radio frequencies between users of different radio frequency communication systems. A problem with this method is that the users of one communication system may sometimes interfere with the users of another communication system sharing the same radio frequencies. Accordingly, some known frequency sharing schemes allocate a radio frequency channel to one or more stationary users located in a first geographic area. The same radio frequency channel is then allocated to other stationary users located in a second geographic area that is far enough away from the first geographic area to prevent interference between the users of the two different systems. This frequency sharing scheme, however, is only workable for communication systems in which the users are stationary and do not roam into areas wherein interference will occur between users of the different systems.
Thus, what is needed is a frequency sharing scheme for mobile users that prevents interference between users of different communication systems sharing the same radio frequency channels.